1. Technical Field
The present invention relates to network interfacing and more particularly, to networks and systems controlling network data traffic on half-duplex networks.
2. Background Art
Local area networks use a network cable or other media to link stations on the network. Each local area network architecture uses a media access control (MAC) enabling network interface cards at each station to share access to the media.
The Ethernet protocol ISO/IEC 8802-3 (ANSI/IEEE Std. 802.3, 1993 edition) defines a half-duplex media access mechanism that permits all stations to access the network channel with equality. Traffic is not distinguished or prioritized over the medium. Each station includes an Ethernet interface controller that uses carrier-sense multiple-access with collision detection (CSMA/CD) to listen for traffic on the media The absence of network traffic is detected by sensing a deassertion of a receive carrier on the media. A station having data to send will attempt to access the channel by waiting a predetermined time after the deassertion of a receive carrier on the media, known as the interpacket gap (IPG) interval.
In a traditional half-duplex Ethernet environment, stations contend for access whenever they have a packet to send. If all the stations transmit data to be transmitted on the network such that each station can saturate the network, the overall effect of throughput decreases due to collisions on the network. For example, if two stations simultaneously transmit data on the network, the two stations will collide, halt transmission, and enter a collision mediation, where each station will wait a random number of slot times calculated according to the truncated binary exponential backoff (TBEB) algorithm before attempting access of the media. Hence, an increased number of collisions decreases the overall effective throughput of the network.
Theoretically, each station will on average receive a percentage of throughput which could be on the order of 1/N, where N is the number of stations on the network. However, without any form of integrated mediation, it is not possible to ensure that some stations get higher bandwidth than others. Hence, the network stations are uncoordinated in that each network station will attempt to transmit data when the network media is available, disregarding the bandwidth requirements of other network stations.